This proposal is a request for a Research Irradiator for the shared use of investigators across the University of California, Los Angeles campus. The equipment requested is a self-contained research irradiator with a cesium 137 source with a nominal content of 6,000 Ci. This piece of equipment will be used for irradiation of biologic research samples by over 200 investigators who work under the auspices of 40 NIH-USPHS investigators at the UCLA Westwood campus. This unit is requested to replace a research irradiator source that is now 25 years old. The present old piece of equipment is used on an average of 250 times per month by individuals from these 40 NIH supported laboratories. We have a compelling need for new equipment because of problems with the present, very old irradiator. The source, being quite old, now continues to have ongoing mechanical breakdowns because of wear to the instrument. These breakdowns are costly in terms of lost research because it may take several days to repair, during which time experiments that had been initiated, are unable to be performed and are often lost. Additionally, the radiation source has decayed to the point that delivery rates are very slow causing difficulties in timely access for investigators with our present amount of use. The unit is so old that its manufacturer will not recharge the source. The new irradiator requested will have more rapid delivery, a longer half life (Cesium vs. Cobalt), has improved operational and safety features and should be free of the mechanical problems of the old equipment. The old irradiator will be kept as a back- up to be used should the new piece of equipment become unserviceable at any time and thereby prevent the loss of any initiated experiments. Thus, the provision of this new research irradiator will maintain an extremely valuable resource in the research infrastructure for investigators campus- wide at the University of California, Los Angeles.